This invention is concerned with the fabrication of microstructures composed of multiple substructures which must be prepared using incompatible processing steps but which must be integrated in close physical association in the ultimate microstructure end product.
Suspended microstructures have been developed for a variety of applications, primarily those requiring thermal or mechanical isolation for their operation. In the thermal isolation category, the microbolometer is probably the best example. A microbolometer uses an array of small thermal sensors which is suspended above a multiplexing integrated circuit using conventional surface micro machining techniques.
The category of devices suspended for mechanical isolation includes many micromechanical applications. Numerous discrete devices, such as accelerometers, gyroscopes, microphones, pressure sensors, and moving mirror displays, have been made using both surface and bulk processing techniques.
The current state of the art for infrared bolometer arrays is best represented by the Honeywell process, which involves the deposition, etching, and patterning of various materials directly on top of a silicon integrated circuit. Because of the sensitivity of the integrated circuit to such conditions as high temperature, ion bombardment, or chemical environment, these additional processing steps are severely restricted. Compromises are required in the processing, the selection of materials, and the resulting device quality.